I went to Clay Shirky's talk, Ontology Is Overrated, at the ETech conference in San Diego in March, and it was one of the highlights of the show. Assuming you missed it, you can now read an expanded version on Clay Shirky's Writings About the Internet, here. It runs from the periodic table of elements to Delicious, and if you haven't come across these ideas before, it probably will change the way you see the world.